function [ Sf ] = Period( xn,f,N )
%PERIOD Summary of this function goes here
%   Detailed explanation goes here
n = (0:1:N-1);
if(size(xn) ~= N)
    disp('The size of data x(n) is not N!');
else
    ss = xn*exp(-j*2*pi*n'*f);
    Sf = (xn*exp(-j*2*pi*n'*f)).*(xn*exp(j*2*pi*n'*f))/N;
    Sf = pow2db(Sf);    
end
end

